This invention relates generally to systems which utilize thermal energy available in furnace gases to pre-heat water being supplied to a water heater from a cold water source.
Generally speaking, such systems are known in the prior art. For example, see U.S. Pat. No. 2,166,355 issued to L. J. Higgins et al on July 18, 1939 which employs a coiled water pipe disposed within a furnace flue or duct to circulate water from the top of a water tank to the bottom thereof to raise the temperature of the water in the tank. Another such prior art system is disclosed in U.S. Pat. No. 3,896,992 issued to A. Borovina on July 29, 1975 wherein hot water from a water heater is supplied directly to water faucets through a coiled water pipe disposed within a furnace. Yet another such prior art system is disclosed in U.S. Pat. No. 3,999,709 issued to P. S. Estabrook on Dec. 28, 1976 wherein water is circulated from a water heater through a heat exchanger located in a furnace chimney and back to the tank once again by means of a pump.
One difficulty encountered in such prior art systems is the necessity of using a pump to force the circulation of water through the heat exchanger.
Another difficulty encountered is the inefficient circulation of water in a closed loop between the hot water heater or storage tank and the furnace heat exchanger.
My invention substantially overcomes these and other prior art problems.